The amount of information being created and retained in the world continues to increase, seemingly at a geometric pace. Individuals take photographs and store them digitally. Corporations maintain databases of reports, presentations, and analyses. Furthermore, different entities of all types are making much of their information available via the Internet.
Although so much of the world's information is now accessible over the Internet, locating a desired item manually is extraordinarily difficult. Instead, search engines are usually used to find information generally and desired items specifically. Search engines review available information, which is a process often termed crawling with regard to the World Wide Web (WWW), to catalog the information into a search index.
A search index facilitates the acquisition of general information and specifically-desired items in an accurate and timely manner. Thus, a search index enables a search engine to locate information that may be of interest to a user. However, there is so much information today that many, many items may be located by a search engine in response to a search query. In the case of the internet, thousands, or even hundreds of thousands or more of such items may be relevant or may appear to be relevant to a user's interest as expressed in the search query.
An issue for search engines therefore becomes one of ranking the relevant items. The items are hopefully ranked such that more relevant items are ranked higher than less relevant ones. Many search engines are now relatively proficient at finding items that are potentially relevant to a user's expressed interest. Unfortunately, search engines still often fail to rank relevant items in accordance with a user's level of interest in them. Especially when many potentially relevant items are located by a search engine, the inability to properly rank them can be disappointing and dissatisfying to users.